1. Field of the Invention
The present invention relates generally to an apparatus for providing signals indicative of the rotation position of a rotary shaft, such as the shaft on a control valve, and more particularly to an improved rotary shaft position indicating mechanism incorporating a visual display of the shaft position and having self-centering parts.
2. Discussion of the Prior Art
U.S. Pat. No. 4,962,290 which is assigned to the present applicant discloses a rotary shaft position indicating switch assembly adapted to be mounted on a valve or a pneumatic valve actuator having a rotary shaft projecting therefrom. The assembly includes a frusto-conical member which is selectively secured to the underside of the base by a set screw, and which is downwardly and outwardly flared. A rotatable second frusto-conical member is concentrically disposed within the confines of the first frusto-conical member and includes graphics information thereon viewable through a window area.
Automax, Inc. of Cincinnati, Ohio manufactures and sells a rotary shaft position indicator in which a cam shaft passes through the base portion thereof and is journaled for rotation therein. A shaft passes upward through the housing cover and into a plastic dome having an inner member containing printed graphics information secured to the cam shaft. The outer member of the dome is generally opaque except for a transparent window through which the graphics information can be read.
The Automax device includes only a single window through which the graphics information can be observed and thus is only viewable when the observer is positioned in the limited zone. Further, the dome can only be removed by using a tool such as a screwdriver to facilitate access to the internal cams and switches. Thus, the dome has to be visually and carefully oriented every time it is snapped back onto the cover. This requires the operator to pay careful attention to what percentage of the "open" or "closed" indicia should be observable through the window when the dome is eventually reassembled to the cover. Thus, a careless operator or serviceman could inadvertently reassemble the graphics information of the dome at an orientation 90 degrees from the intended position, thus indicating an inaccurate valve position.
Another company, Proximity Controls, Inc., of Fergus Falls, Minnesota, manufactures and sells a line of valve position indicators including a mechanical display. In the Proximity Controls, Inc.'s devices, the visual indicator is mounted to the switch enclosure at a location between the valve being monitored and the switches. The indicator is made of two plastic drums, one inside the other, where the inner drum includes words, symbols or other graphics which may be viewed through a window formed in the outer drum. However, this indicator suffers from the drawback that the visual indicator is physically located between the valve being monitored and the switches and thus, is not observable from a position 360 degrees around the indicator. Moreover, the entire switch enclosure needs to be removed from the valve being monitored to make adjustments to the indicator. Finally, there is only one window designed in this indicator and there is no teaching that the window can be rotated such that it can be viewed from more than one perspective.
The design of the Proximity Controls rotary shaft position indicator suffers from the draw back that the visual indicator is viewable from only one perspective. Further, each window must be carefully aligned each time the respective window drums are reassembled to the housing, which is time consuming and prone to alignment errors. Both indicators require the user to use a separate tool to disassemble the indicator which can be both frustrating and clumsy. Finally, neither of the devices includes an electronic display.
Westlock Control Corporation of Moonachie, N.J., also manufactures and sells a line of valve position indicators as disclosed in U.S. Pat. No. 4,494,566. The device includes an inner drum having colored sections coordinating with the colored housing. This patent teaches only a mechanical display arrangement, and fails to teach any keying arrangement or an electrical display, or any color coordination with an electrical display.
Valve Conversions Limited of the United Kingdom is the owner of patent GB 2,229,254 which is similar to the Westlock device. It teaches various mechanical arrangements for color coordinating an inner drum with a housing. Again, this device fails to teach a keying arrangement, and also fails to teach an electronic display.